The present invention relates generally to oil and gas wells and, more specifically, to a system for removing casing which has been placed in a well bore.
The process of drilling subterranean wells to recover oil and gas from reservoirs, consists of boring a hole in the earth down to the petroleum accumulation in the reservoir, and installing pipe from the reservoir to the surface. Casing is a protective pipe liner within the well bore that is cemented in place to ensure a pressure-tight connection to the oil and gas reservoir. The casing can be run from the rig floor as it is lowered into the well bore. After the casing has been run to the desired depth it is typically cemented within the well bore. The purpose of cementing is to seal the casing to the well bore formation.
Sometimes after a string of casing has been cemented, it must be removed for one or more reasons (such as plug and abandoning the well bore or removing the casing so that the well can be redrilled, called sidetracked, if for some reason the drill bit cannot pass through the previously installed casing or matter located downhole). This invention potentially saves several hours of drill rig time (from 2 hours to ½ hour) for removing the casing and is used for removing casing that was previously cemented in place. Removing the casing is a difficult job because of the tremendous amount of force which must be placed on the casing to pull it out of the ground. The casing was cemented in the ground generally to keep it in place. Accordingly, not only must the weight of the casing be pulled out of the well bore, but also the weight of the cement along with overcoming the frictional forces caused by the cement interacting with the sidewall of the well bore.
In prior art systems the casing was removed by incremental sections, such as forty foot increments. For an incremental section of casing, casing operators would cut the casing and manually drill two holes. The two holes were drilled on either side of the casing attempting to have them aligned with each other. After the holes had been drilled, a bar or rod would be placed through the two holes. The bar or rod would then be pulled up by the rig's top drive unit or the draw works a specified incremental amount, such as forty feet. As discussed above, in raising the casing a tremendous amount of force was required to overcome the resisting forces. After the incremental section of casing had been raised, the cutting and drilling process would start over again for the next incremental section of casing. After the various increments of casing were cut and pulled from the well bore, they would be disposed of.
In prior art systems, operators would attempt to individually and sequentially drill the two holes in each incremental section of casing. The operator would first drill one side. Depending on the thickness of the wall to be drilled, drilling would have to be intermittently stopped and all drilled material removed from the drill bit. This process would take much time and slow down the removal of the casing (such as 2 hours). Second, the operator would go around to the other side of the casing and attempt to drill a second hole opposite the first hole. Again, intermittent breaks to unclog the drill bit would be required. Sometimes, the operator got lucky and the two holes lined up, but at other times the two holes did not line up and a bar could not be inserted through both holes. When the two holes did not line up, the operator using a torch would have to chip and cut at least one of the holes to open it up so that the bar could be placed through both holes.
This process took much rig time and created a hazardous working environment when using a torch and was potentially repeated for each incremental section of casing.
While certain novel features of this invention shown and described below are pointed out in the annexed claims, the invention is not intended to be limited to the details specified, since a person of ordinary skill in the relevant art will understand that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation may be made without departing in any way from the spirit of the present invention. No feature of the invention is critical or essential unless it is expressly stated as being “critical” or “essential.”